1. Field of the Invention
The present invention generally relates to AC induction motors, and more particularly to a coreless AC induction motor that employs a cup-type coreless rotor made of an aluminum or copper conduction cylinder so as to reduce the inertial force of the rotating parts of the AC induction motor.
2. Description of the Prior Art
In general, a cup-type coreless rotor is utilized in a small-capacity DC motor for low power output, but is not used in the field of a large-capacity AC motor.
In a rotating body such as rotor of motor, a centrifugal force is generated in proportion to the mass of a rotor and the square of the rotational speed of a rotor, so that a rotor with high rotating speed may have excessive deformation due to a large stress by the centrifugal force.
The quality of machined products mainly depend on the precision of machine tool which is equipped with built-in type spindle system that is composed of the rotor of motor and the spindle shaft, but the heavy mass of rotor can deteriorate dynamic stability of the built-in type spindle system because the heavy mass of rotor may cause excessive stress and deformation. Therefore, it is important to reduce the inertial force of the rotor by reducing mass of rotor.
The rotating speed of a built-in type spindle generally is restricted by a DN value (where D is a bearing nominal diameter in mm and N is the revolutions per minute of the spindle) and the critical whirling vibration frequency of the spindle. In particular, in the case of a built-in type spindle which is composed of the spindle shaft and the rotor of motor, the bending natural frequency is largely influenced by the mass of the rotor of a motor. Accordingly, as the mass of the rotor of a motor is increased, the bending natural frequency of a built-in type spindle is decreased, thus the heavy mass of rotor limits the maximum rotating speed of the built-in type spindle.
Accordingly, in order to get stable driving condition of a built-in type spindle, it is necessary to increase the specific bending stiffness of a spindle shaft or to decrease the mass of rotor of a motor.
Accordingly, the present invention considers the above problems occurring in the prior art, and an object of the present invention is to provide a coreless AC induction motor that employs a cup type coreless rotor made of an aluminum or copper conduction cylinder so as to reduce the inertial force of the rotating parts of the AC induction motor and to allow the motor to have high speed and low rotational inertia.
Another object of the present invention is to provide a coreless induction motor that employs an air bearing, thereby preventing direct contact between rotating parts and stationary parts and dissipating generated heat during the operation of the motor.
In order to accomplish the above object, the present invention provides a cup-type coreless AC induction motor, comprising: a cup-type coreless rotor; a rotating shaft combined with the cup-type coreless rotor; a stationary induction rod inserted into the interior of the cup-type coreless rotor to guide a magnetic flux from stator coils; and a stator positioned around the coreless rotor; wherein the cup type coreless rotor comprises a squirrel cage-shaped conduction cylinder and composite material or polymer resin; the squirrel cage-shaped conduction cylinder is made of material having high electric conductivity, such as aluminum or copper and has regularly plurality of slots along the axis of the conduction cylinder; The slots of the squirrel cage-shaped conduction cylinder may be filled with the composite material or polymer resin in order to make up for the low stiffness of squirrel cage-shaped conduction cylinder.
In accordance with a feature of the present invention, the composite material or polymer resin includes powder having high magnetic permeability, such as iron or ferrite powder, to make up for the low magnetic permeability of the squirrel cage-shaped conduction cylinder.
In accordance with a feature of the present invention, a motor may include heat pipes, the heat pipes can be inserted into the slots of the cup type squirrel cage-shaped conduction cylinder so as to dissipate heat generated effectively.
In accordance with a feature of the present invention, the motor further comprises bearings, the bearings being positioned between the cup type squirrel cage-shaped conduction cylinder and the induction rod to align the squirrel cage-shaped conduction cylinder with the induction rod and positioned between rotating shaft and motor housing to support rotating shaft.
In accordance with a feature of the present invention, the induction rod has an air supply bore in its central portion and also has plurality of air bearing holes connected with the air supply bore, so that supplied air functions as a bearing between the coreless rotor and the induction rod.